Ukrainian forces began military operations in the east of the country Tuesday , marking a definite end to a unilateral cease-fire that had been in place for 10 days .

The speaker of Ukraine 's parliament , Oleksandr Turchynov , told lawmakers the government 's `` anti-terror operation '' against pro-Russia separatists had been `` renewed . ''

Ukrainian armed forces have been conducting `` attacks on terrorists ' bases and defended posts , '' he said .

The announcement came hours after Ukrainian President Petro Poroshenko said that his country would not renew a cease-fire with the separatists , vowing instead to `` attack and liberate our land . ''

`` Termination of cease-fire is our response to terrorists , insurgents , marauders ... and -LRB- those who -RRB- deprive people of normal peaceful life , '' Poroshenko said .

In a statement on his website , Poroshenko congratulated Ukraine 's armed forces and border guards for re-establishing control over the checkpoint at Dolzhanskyi , in `` the first victory since the restoration of the CTO , '' a reference to the government 's Counterterrorist Operation . He said the armed forces and the State Border Service of Ukraine regained control over the checkpoint and combat engineers removed mines from the checkpoint and adjacent roads .

Violence flared Tuesday in Donetsk , one of the cities at the heart of the separatist unrest .

Interior Minister Arsen Avakov , on his official Facebook page , said that militants had launched an attack on a regional police headquarters building in Donetsk , killing one police officer and badly injuring two more .

Avakov said the police were barricaded inside the building in the city of Donetsk and that the fighting was ongoing .

The Interior Ministry later said three people were seriously injured -- one woman and two special forces policemen . Three others were injured and hospitalized , the ministry said .

Police successfully fought back the attack , the ministry said on its website .

On its website , the Donetsk regional state administration said Ukrainian forces attacked the central part of Kramatorsk from the air and ground . A bus attack in Kramatorsk left four people dead and five others injured . The statement did not say which side in the conflict carried out that attack .

Yuriy Stets , information security head for the National Guard and a parliamentarian , told CNN that the National Guard had regained control of Zakotne , near Slovyansk , and were targeting two other towns .

Cease-fire hopes dashed

The fragile cease-fire expired at midnight Monday , hours after Poroshenko spoke by phone with Russian President Vladimir Putin , German Chancellor Angela Merkel and French President Francois Hollande . Poroshenko also talked on the phone with U.S. Secretary of State John Kerry .

The cease-fire -- agreed on last month amid a volatile political crisis -- raised hopes that Ukraine could be moving back from the brink of full-fledged civil war .

As part of a peace plan , Poroshenko urged the rebels to lay down their arms and engage in talks . He also called for the strengthening of Ukraine-Russia border controls , the freeing of hostages and changes to the constitution to decentralize power .

In his statement , Poroshenko said the militants had failed to take up a `` unique opportunity '' to support the peace plan and had instead violated the unilateral cease-fire more than 100 times .

Putin , addressing Russian diplomats in Moscow , said he regretted the decision to end the cease-fire .

`` Unfortunately , President Poroshenko decided to resume a military operation . I and my EU colleagues could not convince him '' of the need to settle the crisis peacefully .

Putin : ` Only on equal terms '

Putin said Russia had been obliged to annex Ukraine 's Crimea region in March in order to prevent NATO forces entering , which would have created `` a completely different alignment of forces . ''

He told the diplomats that they would `` face growing pressure in defending national interests '' and that `` the events provoked by the West in Ukraine have become a concentrated political expression of deterrence toward Russia . ''

Putin also referred to Russia 's tense relationship with the United States , suggesting that the current crisis was born of the West 's attempts to impose its own way of doing things on the rest of the world .

`` Our relationship with the United States is not the best at the moment , '' he said .

`` We have always tried to be predictable partners , handle business on an equal basis , but in return our legal interests were partially ignored and are still ignored . Russian and U.S. contacts have a great meaning for the entire world .

`` We are ready for constructive dialogue , but again I emphasize only on equal terms . ''

Russia 's ambassador to the European Union , Vladimir Chizhov , said Tuesday that the refusal to extend the cease-fire is a `` negative sign , '' the Russian Foreign Ministry said on Twitter .

`` This makes it even harder to understand the logic of how the confirmation of the so-called 15-point peace plan correlates with the refusal to prolong truce , '' Chizhov was quoted as saying by state news agency ITAR-Tass .

` Enemies and invaders '

Poroshenko declared in a late-night televised address that the cease-fire was over .

In Kiev 's Independence Square , known as Maidan , activists outside the presidential administration building applauded Poroshenko 's stance .

`` We need only military actions , '' a priest named Valentyn said in a Reuters interview . `` We were forced by those who entered our country as enemies and invaders . ''

The crisis has its roots in former President Viktor Yanukovych 's decision last year to shun a European Union Association Agreement and turn toward Russia instead . The move unleashed deadly strife that led to Yanukovych 's ouster , Ukraine 's loss of Crimea , and a pro-Russia separatist rebellion . Russia also massed troops along its western border with Ukraine .

The Association Agreement , which will bring closer trade and political ties between Ukraine and Europe , was finally signed by Poroshenko and European leaders last week .

After Monday 's phone call , Poroshenko said his goal was peace but insisted it takes the participation of all parties to maintain stability , noting violations of the cease-fire by pro-Russia separatists .

The Ukrainian government `` has been completely fulfilling its commitments and unilaterally complying with the ceasefire regime for 10 days and paid dozens of lives for that , '' he said .

Peace talks were held last week among Ukrainian government officials , pro-Russia separatists from the restive eastern Luhansk and Donetsk regions , Russian officials , and members of the Organization for Security and Cooperation in Europe .

` Bloody truce '

Activist Vadym told Reuters there was no point in continuing the cease-fire .

`` There is definitely no need for an extension of the truce , '' he said . `` Because a lot of our boys died during this truce . ''

Fellow activist Yulia agreed .

`` Bloody military actions are better than such bloody truce , '' she said . `` We must put an end to it once and that 's all . ''

A statement from Putin 's press office about the call said the Russian President `` stressed the need to extend the cease-fire and also establish a reliable mechanism for monitoring '' it .

Ukrainian President : Peace depends on Putin 's mood

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Interior minister says militants have attacked police HQ , causing police casualties

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Putin says he tried to persuade Poroshenko to resolve crisis through peaceful means

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Speaker tells Parliament that Ukraine military has restarted operation against militants

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Poroshenko declares an end to a unilateral cease-fire with pro-Russian separatists